1. Field of the Invention
The present invention relates to a technology for detecting a tilt of an original in a sheet-through type reading device in an image processing apparatus.
2. Description of the Related Art
An image reading device mounted on a scanner, a facsimile, or a digital multifunction peripheral is generally configured as either a flat head type or a sheet through type depending on a method of reading an original. Specifically, the flat head type image reading device scans an entire original by moving a line sensor while the original is placed at a fixed position. On the other hand, the sheet through type image reading device scans an entire original by moving the original while a line sensor is placed at a fixed position. Recently, a sheet-through type image reading device provided with a line sensor for reading a front surface of an original and a line sensor for reading a back surface of the original on a conveying path of the original is becoming popular. However, the sheet-through type image reading device reads an original by moving the original, so that the original is more likely to tilt with respect to a reading direction while the original is read compared to when the flat head type image reading device is used.
With regard to a tilt of an original in the sheet-through type image reading device, Japanese Patent Application Laid-open No. H11-298682 discloses a technology for detecting a tilt of an original by using a dedicated sensor. Specifically, the dedicated sensor that detects an edge of the original is provided on a conveying path of the original with respect to each size of the original. Furthermore, Japanese Patent Application Laid-open No. H7-262312 discloses a technology for detecting a tilt of an original based on a connectivity of black pixels contained in the original that has been read.
However, in the former technology, the dedicated sensor that detects the edge of the original needs to be mounted on the image reading device in addition to a line sensor that reads the original. Therefore, the size of the image reading device and costs for hardware increase.
In the latter technology, an image recognition process is necessary. Therefore, when the image recognition process is performed by software, a processing time increases, and when the image recognition process is performed by hardware, a large-scale and complicated circuit is necessary. Furthermore, when a character line printed on the original is initially tilted with respect to each side of the original, a tilt of the original cannot be accurately detected.